1. Field of the Invention
The present invention relates to a coordinate input apparatus and, more particularly, to a coordinate input apparatus for detecting the position of a coordinate input pen which was pressed at a desired position on a coordinate input plate and for-outputting to a target apparatus.
2. Related Background Art
In recent years, a system for recognizing hand writing characters and figures in an on-line manner attracts attention as a system which can realize a man-machine interface of the next generation. In a hand writing recognition system, a coordinate input apparatus and a display are arranged so as to overlap and the trace of the characters or figures which are hand written by a pen-shaped indicator is displayed as it is by the display. That is, characters, figures, etc. can be input as if they are hand written onto a paper.
In such a system, the coordinate input apparatus is controlled in a manner such that the coordinate value data which was digitized at a necessary resolution is sampled every predetermined period of time and the coordinate value data is stored in a predetermined area in a memory device or transmitted to a main information processing apparatus through communicating means for every sampling operation. A group of coordinate value data is hereinafter referred to as dot train data.
It is improper that the main information processing apparatus for recognizing characters or the like directly uses the stored or transmitted dot train data in the original form.
In other words, it takes a certain amount of time to calculate the coordinate value data. Therefore, during the calculation of the coordinate value data, the coordinate position which is indicated by an input pen fluctuates and an oscillation occurs because, for instance, the input pen is slightly lifted up or the input pen slightly slides or the like. Even in such a case, there is a problem such that when the coordinate value is calculated on the basis of a voltage value or the like and is used as an input coordinate position in a manner similar to an ordinary case, a coordinate value data which is not desired by the operator is input.
In the coordinate input apparatus of the resistive sheet type, the ultrasonic vibration type, or the like which can easily construct a tablet surface from a transparent member, the fluctuation of the detection coordinates is large in a transient state of a writing pressure just after the pen-up operation, just before the pen-down operation, and the like. The above dot train data also includes the data in the transient period of time of the writing pressure.
Since such a fluctuation of the coordinate value data is fairly, inconvenient in the recognition of characters or figures, after one character or one figure was completely input, dot train data in which factors of such a fluctuation were eliminated from the dot train data obtained by the input of the character or figure must be newly reconstructed and the process to recognize the character, figure, or the like must be executed on the basis of the reconstructed dot train data.
However, such a method has the following drawbacks.
1) In addition to an area to store the dot train data, another area to store the dot train data which was reconstructed by eliminating the fluctuation factors is needed. PA1 2) In the case of a character or a figure such as a Chinese character or the like in which the number of strokes is large and a number of complicated component elements exist, it takes a fairly long time to execute the process to eliminate the fluctuation factors.
The above drawbacks also cause, for instance, deterioration of a recognition ratio and a recognition speed of characters, figures, or the like.